A number of different ways for disposing of waste have been extensively used. Landfilling and incineration are the major ones. However, these methods do not seem to offer the best solution for many wastes.
Landfilling is becoming less and less desirable since it does not offer elimination of waste, but just underground storage. Thus, it has started to be used more for by-products of other types of waste management, such as incineration for example, than for landfilling the primary waste.
Incineration, requiring oxidation of waste at high temperatures with high volumes of air, followed by separation of the effluent gases from the produced ash and the entrained particulate matter, becomes involved, complicated, and expensive, despite the fact that at first glance it sounds to be a simple process of "just burning the waste".
In recent years, a new method, based on supercritical water oxidation, has been developed. The new method achieves substantially complete oxidation of waste by using higher reaction temperatures in conjunction with certain phase properties of water. This method results in fairly compact equipment and is an excellent candidate for on-site disposal. Supercritical water oxidation also has the advantage of producing a clean water product suitable for process recycle, thereby facilitating waste minimization. However, as with the development of any new process or equipment, there are numerous problems which have not been resolved so far, and which are vital for a finally successful use and commercial exploitation.
In a water liquid/vapor phase diagram, one may see that there is a critical point of temperature (about 705.degree. F.) and a critical point of pressure (about 3,200 psia) over which there is only one single fluid phase, and which, although it represents neither liquid nor vapor, behaves and seems to have more of a gas character than of a liquid one at pressures near the critical point. At substantially higher pressures, a more liquid-like behavior is observed with an accompanying increase in solubility inorganic matter. The single-phase condition occurring above the critical points is called supercritical condition.
It is worth noting that organic matter decomposes readily under supercritical conditions, and in the presence of oxidant, carbonaceous compounds oxidize substantially completely to carbon dioxide, sulfur compounds to sulfates and nitrogen compounds decompose mostly to molecular nitrogen. It is worth noting that under supercritical water oxidation conditions, only small amounts of nitrogen oxides may be produced, in contrast with incineration which favors the production of nitrogen oxides. Inorganic salts are substantially insoluble in the supercritical water single phase for pressures of the order of 4,000 psia, while it has been reported that they are at least partially soluble at considerably higher pressures, such as 10,000 psia, for example.
The use of very high pressures at elevated temperatures presents a serious problem in the construction of reactors or reaction chambers which can withstand these adverse conditions. It is well known that as the temperature increases, the strength of materials decreases drastically. Supercritical pressures (greater than about 3,200 psia) at temperatures exceeding about 1,000.degree. F. present an enormous challenge to any construction material, let alone higher pressures (of the order of 10,000 psia) and temperatures, which may be desirable for a number of reasons, including dissolution of inorganic salts in the supercritical single phase. If in addition to the temperature/pressure challenge, one considers the harsh environment inside the reaction chamber, the problem becomes very serious.
Thus, it is extremely important to improve the waste removal efficiency of such reaction chambers as much as possible. In general, control of reaction temperature is essential in maintaining control of many reaction processes and, therefore, the end results produced by such processes. In some instances, exothermic reactions proceed so rapidly that, unless controlled, they generate temperatures which endanger the integrity of the reaction vessel itself. Many reactions produce reaction by-products which, if the temperature is not properly controlled, may proceed to further undesired secondary reactions. In reactions which occur under pressure and temperature conditions sufficient to achieve supercritical water conditions, salt precipitation and/or other competing side reactions may occur, as aforementioned, unless the heat of reaction is closely controlled. On the other hand, if the temperatures are allowed to fall under certain limits, the reaction products are incomplete, new phases may be formed in the reaction zone, or the reaction may cease to take place altogether.
Reaction temperatures of exothermic reactions are generally controlled by limiting the rate of reaction For example, over-all reaction rate can be limited by gradual mixing of reactants so that the one reactant and/or the reaction vessel absorbs energy from the reaction and transfers that energy to an external sink by cooling the reaction vessel or the like. Such processes, however, are difficult to control and cannot be readily or economically applied to many reaction conditions.
A number of patents have dealt with supercritical water oxidation of coal, organic substances, and waste, among which are U.S. Pat. Nos. 4,292,953 (Dickinson), 4,141,829 (Thiel et al.), 4,338,199 (Modell), 4,543,190 (Modell), 4,564,458 (Burleson), 4,594,164 (Titmas), 4,792,408 (Titmas), 4,822,394 (Zeigler et al.), 4,822,497 (Hong et al.), 4,861,497 (Welch et al.), 4,891,139 (Zeigler et al.), 5,075,017 (Hossain et al.), 4,113,446 (Modell et al.), 4,338,199 Reexamined (Modell), 5,106,513 (Hong), 4,983,296 (McMahon et al.), 5,011,614 (Gresser et al), 5,053,142 (Sorensen et al.), 5,057,231 (Mueller et al.), 5,106,513 (Hong), 5,133,877 (Rofer et al.), 5,183,577 (Lehmann), 5,192,453 (Keckler et al.), 5,221,486 (Fassbender), 5,232,604 (Swallow et al.), 5,232,605 (Baur et al.), 5,240,619 (Copa et al.), 5,250,193 (Sawicki et al.), and 5,252,224 (Modell et al.).
None of these references has resolved or even has attempted to resolve the vital aforementioned problems, in contrast with the present invention, which uses critically spaced side ports to inject critical amounts of oxidant and water, in addition to other criticalities, in order to alleviate such problems by considerably improving the output of reaction chambers operating in the vicinity of supercritical water conditions, as set forth in detail hereinbelow.
U.S. Pat. No. 1,988,456 (Lysholm) discloses a gas turbine system, wherein fuel is introduced, through a number of nozzles, into a stream of air. Water may be sprayed in the gas turbine in order to reduce production of soot and to maintain the temperature under a permissible maximum. In addition, no criticality is disclosed or implied regarding the spacing between nozzles.
Enhancement of the reaction rates and therefore reaction efficiency by reactant concentration and temperature control is not disclosed, suggested or implied.
U.S. Pat. No. 3,549,314 (Shah) discloses a method of oxidizing black liquor in a sinuous or duct oxidizer, by dispersing an oxidant containing gas into the continuous black liquor phase flowing within the duct. The gas is passed into the black liquor at spaced intervals, and the resulting dispersion in oxidized black liquor is discharged into a vessel below the level of the body of liquor in the vessel. The ports through which the gas enters the oxidizer are preferably, as evidenced by Shah's FIG. 1, are equidistantly spaced, and it appears that substantially the same amount of oxidant-containing gas passes through each and all ports. The multiplicity of ports apparently serves the purpose of producing as many gas bubbles as possible in order to maximize the degree of oxidation of the black liquor. No criticality is disclosed or implied regarding the distance between ports, or the amount of oxidant entering through each particular port. Further, no temperature control is needed or used.
U.S. Pat. No. 3,654,070 (Pradt et al.) discloses a method of oxidizing organic material in spent liquor. The spent liquor from the pulping of cellulosic material by oxidation in an aqueous medium is subjected to oxidation with an oxidant-containing gas at a temperature between 200.degree. and 375.degree. C. This process oxidizes the organic waste products to carbon dioxide and regenerates the aqueous alkaline medium for reuse in the pulping process
U.S. Pat. Nos. 4,898,107, 4,714,032, 4,593,202, 4,380,960, and 4,377,066 (all to Dickinson) disclose recirculation of water to a reaction chamber or air injection in one or more side ports, however, indiscriminately spaced.
U.S. Pat. No. 4,721,575 (Binning et al.) discloses a method for effecting accelerated chemical reactions at elevated temperatures and pressures including wet oxidation of materials in waste streams. Multiple injection and extraction points are provided along the path of the tubular reactor coil used to permit gas, liquid or solid reactants to be added or extracted as desired.
None of the above references disclose, suggest, or imply the criticalities of the instant invention. In contrast to these references, applicants have found critical relationships, as set forth hereinbelow, which result in highly improved reactor chambers and reactor assemblies for waste water treatment to yield innocuous products of reaction with considerably improved output.